The invention refers to a clamping chuck having a central receptacle and a disk which surrounds the receptacle and which may be moved to a clamping position wherein a drawbar inserted into the receptacle is clamped, and to a releasing position wherein the drawbar is released, the disk comprising a catch mechanism having circumferentially equally spaced catch elements, the chuck further having a blocking means which aggravates movements of the disk under the influence of an axial load on the clamped drawbar.
The document EP 0255042 discloses a clamping chuck which is equipped with a ball catch having a plurality circumferentially equally spaced balls wherein for each ball a radial (with respect to the central axis of the receptacle) pocket is provided within a disk surrounding the receptacle. The disk may be transferred from the releasing position to the clamping position by a driving medium, e.g. compressed air. During such transfer the balls are urged radially against the drawbar thereby engaging from below an oblique ring surface of a radial drawbar incut provided near the the end thereof. An automatic return of the balls into the pockets under the influence of an axial load on the drawbar is prevented by the drive means. Only in case the draw bar may be released the disk is no longer under clamping pressure.
The axial load on the draw bar may be high if a workpiece mounted to the draw bar is machined by cutting. The axial load is substantially lower if the workpiece is machined by electroerosion.
Manually operated clamping chucks have a handle which projects to the exterior of a housing through a slot thereof. The handle may be pivoted within a plane which extends transverse to the central axis of a receptacle of the chuck. The handle may be manipulated such that the disk is rotated to its clamping position or such that the disk is rotated to its releasing position. A blocking means is provided which prevents that the disk escapes its clamping position under the influence a high load on the clamped draw bar when the handle is left free. The blocking means may include a brake surface on the disk which is in frictional contact to an inner surface of the housing surrounding the catch mechanism. It is necessary that the disk is held safely in its clamping position for ensuring that the draw bar remains fixedly clamped under all operating conditions. The brake force developed by the blocking means should therefore be sufficiently great. A high brake force, however, aggravates manual manipulation of the handle and, apart therefrom is not necessary for electroerosive machining of the workpiece.
It is an object of the invention to create an improved clamping chuck. According to a further object of the invention the risk of an escape of the disk from its clamping position specifically under the influence of a high load on the clamped draw bar is excluded or at least substantially decreased while the handle may be manipulated easily.
The improved clamping chuck according to the invention comprises a central receptacle for receiving a draw bar, and a disk member which surrounds the receptacle and which may be moved to a clamping position wherein the draw bar inserted into the receptacle is clamped, and to a releasing position wherein the draw bar is released from being clamped. The disk member comprises a catch mechanism having circumferentially equally spaced catch elements. A blocking means is provided which develops a brake force for preventing movement of the disk member once it is transferred into its clamping position. The amount of developed brake force is made dependent from the amount of an axial load on the draw bar such that a high axial load causes a high brake force and a low load causes a low brake force.
The invention is advantageous therein that the draw bar is held automatically in its clamped position because axial loads on the draw bar produce the necessary brake force preventing a displacement of the disk. Moreover it is advantageous that the disk may be manipulated from the releasing position into the clamping position thereof and vice versa by hand without substantial effort. Specifically, without a load on the draw bar there is no braking effect.
The invention allows for a number of preferred embodiments. The blocking means may be made as an axially operating brake or as a radially operating brake. The axial brake is preferably made such that a brake disk is put upon the disk which is rotatably and axially immovably held within the housing. The brake disk abuts under friction a radial inner surface of the housing and is coupled to an oblique ring ramp of the draw bar. Such coupling may be established by the catch elements which may be balls.
The radial brake made be made preferably such that radially elastic segments are mounted to the disk which abut under friction an axial inner surface of the housing. Each segment is coupled to the oblique ring ramp of the draw bar upon clamping thereof. Such coupling may be realised by the catch elements, which are preferably balls.
The radial brake may be formed from a disk which is only rotatable as well as from a disk which can be moved only axially. In the last mentioned case the disk is connected to a handle which extends through an axial slot in the housing wall. The handle may be manipulated axially.
Apart from the above, preferred embodiments of the invention are defined in the subordinate claims. Embodiments of the invention are described in detail with reference to the appending drawings.